A spherical particle of radius r1 experiences uniform thermal generation at a rate of q. The particle is encapsulated by a spherical shell of outside radius r2 that is cooled by ambient air. The thermal conductivities of the particle and shell are k1 and k2, respectively, where k1 = 2k2. By applying conservation of energy principle to spherical control volume A, which is placed at ar arbitrary location within the sphere, determine a relationship between the temperature gradient dT/dr and the local radius r, for O < r